In general, in an image-forming process with an image-forming apparatus employing an electrophotographic technique such as a copier or a laser-beam printer, after a toner image is formed on a transfer-receiving material such as a recording paper sheet through an exposing step, a developing step, and a transferring step, a fixing step of fixing the unfixed toner image to the transfer-receiving material is performed. The fixing process is generally performed by heating and pressing an unfixed toner image to fuse the unfixed toner image with a transfer-receiving material. As for a measure for the heating and pressing, a process is commonly employed in which a fixing roller and a pressing roller are disposed so as to face each other, and a transfer-receiving material on which an unfixed toner image is disposed is passed between the rollers to press the unfixed toner image between the rollers and to heat the unfixed toner image by using a heating source installed in the fixing roller.
Japanese Unexamined Patent Application Publication No. 5-40425 discloses a process in which a steel use stainless (SUS) tube is used as the fixing roller. However, SUS tubes are expensive in terms of material cost and processing cost and hence have a problem of the costs. SUS tubes also have a problem in that SUS tubes have poor flexibility and hence end portions and the like of the SUS tubes tend to suffer from cracking, for example, when paper sheets are caught in the SUS tubes.
In recent years, as illustrated in FIG. 1, a process in which an unfixed toner image 5 on a transfer-receiving material 4 is heated with heating means (heater) 2 through a thin endless belt 1 (fixing belt) and pressed with a pressing roller 3 to fix the unfixed toner image 5 to form a fixed toner image 6 has been developed. Such a fixing belt is commonly an endless belt in which a polyimide tube, which is excellent in terms of heat resistance, mechanical strength, tear strength, flexibility, a mold release property, and the like, is used as a base member and a fluorocarbon resin layer is disposed on the outer surface of the base member.
To improve the thermal conductivity of a fixing belt in which a polyimide tube is used as a base member and to achieve, for example, a decrease in waiting time after the turning-on of power, a decrease in power consumption, an increase in fixing speed, and a decrease in fixing temperature, a process in which the polyimide tube is made to contain an inorganic filler that is excellent in terms of thermal conductivity has been disclosed. Such inorganic fillers proposed are carbon black, silicon carbide, silica, and the like (Japanese Unexamined Patent Application Publication No. 3-25478); boron nitride (Japanese Unexamined Patent Application Publication No. 8-80580); carbon nanotubes (Japanese Unexamined Patent Application Publication No. 2004-123867); and the like.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 5-40425
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 3-25478
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 8-80580
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2004-123867